- Scientists from the USDA’s Agricultural Research Service (ARS) have identified five varieties of romaine lettuce that brown and deteriorate slower after being harvested. These are Darkland, Green Towers, Hearts Delight, Parris Island Cos and SM13-R2, which is a breeding line developed at the ARS lab.
- Researchers identified the location of the genes associated with post-harvest deterioration and are working on pinpointing those associated with browning.
- Additionally, the scientists found four genes that are linked with resistance to one of the most economically costly lettuce diseases: downy mildew.
Lettuce is a popular vegetable and one of the top 10 most valuable crops for the United States, with a farm gate value of more than $2.5 billion in the United States in 2017, according to the USDA. That year was also the year that fresh lettuce consumption peaked at 12.5 pounds per person, up from 12 pounds in 2006, according to Statista.
Romaine lettuce sales have significantly wilted in the last two years, after the green has been linked to five separate E. coli outbreaks. It is typically the most widely consumed salad green, but sales slumped 13% in 2018 to $631 million, according to data from Nielsen.
Still, lettuce remains a popular leafy vegetable as evidenced by the surge in the prices of other varieties, which saw a 170% jump in 2018, according to the USDA. Producing a lettuce that remains green for longer may provide some visual reassurance to consumers who are looking for the freshest heads of lettuce at supermarkets. It may also allow producers to process the crops more carefully, knowing that the shelf life of the vegetable is longer.
According to the University of California at Davis, the shelf life of lettuce stored at 32°F is 21 days. When stored at 41°F, the shelf-life is about 14 days. Achieving longer periods of shelf stability is important for fresh foods. According to a recent study from Deloitte, spoilage is a challenge for 32% of retailers. Preserving foods for longer means less waste and greater profits along the supply chain. According to the UN's Food and Agriculture Organization, an estimated 1.3 billion tons of food is wasted or lost to spoilage worldwide annually, which amounts to 4.4 billion tons of annual greenhouse gas emissions.
Not only is reducing food waste important for growers, manufacturers and retailers. It is also important to consumers, who are increasingly shopping with the environment in mind. Consumers are steadily changing their habits to shop more sustainably. Nielsen data shows almost half of U.S. consumers (48%) are likely to change what they buy to meet environmental standards.
Producers have already been working to extend the shelf life of lettuce by using modified atmosphere packaging or flushing bags of cut lettuce with nitrogen gas to reduce oxygen levels. Smart packaging is another approach to extend shelf life, limit spoilage, monitor temperature, detect contamination and track products from their origin to points of delivery. However, these solutions can be costly and lead to other issues such as off odors or anaerobic bacterial growth.
Having lettuce that naturally stays greener and fresher for longer can simplify the process dramatically and also save on packaging costs.
“Having these molecular markers means that slow deterioration and eventually less browning can be more easily integrated into lettuce breeding, traits that are important economic considerations," said research geneticist Ivan Simko with the ARS Crop Improvement and Protection Research Unit in a statement.
This is not the first crop that the USDA has worked to modify in order to improve. Recently the ARS released a mid-season, spring-bearing strawberry variety called "Keepsake" that features a longer shelf-life and a low proportion of decayed fruit after two weeks in cold storage. The government department has also been working to modify other leafy greens with a new red spinach varietal appearing last fall. This red spinach variety features an improved nutritional profile with high levels of beta-carotene, lutein, folate, vitamin C, calcium, iron, phosphorus and potassium.
With consumers continuing to push for more functionality from their food, it would not be surprising if the USDA continues to develop more fresh produce varieties with longer shelf lives.